Will tonight's sky be worth it?

No black box. For your location we read tonight's cloud cover, the moon's brightness, how dark your spot is and how many truly dark hours you get, then weigh them into a single number you can trust.

• Clouds carry the most weight, so a clear night beats everything else. We look at the forecast for the dark hours specifically, not whatever it happens to be doing right now, which is why a clear evening still scores well after sunset.
• Your viewing-spot picker sets how much light pollution sits over the exact place you will stand. A city centre washes out all but the brightest stars, while a dark-sky site shows thousands more.
• The moon's brightness comes from its phase, worked out right in your browser with no lookup. A bright moon costs you points, and we ease off when the moon has already dropped below the horizon.
• The dark window is how long the sky stays genuinely dark after twilight. When you are online we pull tonight's exact twilight times, otherwise we estimate them from your latitude and the date. Near midsummer at far-north latitudes the sky may never fully darken, and we say so plainly rather than show a misleading number.

Each park's rank blends site darkness with how often nights run clear, then scales the result to 0 to 100. Darkness carries about two thirds of the score and clear-night reliability carries about one third, so a very dark park with reliable skies rises to the top.

• Certified means the park or NPS unit appears in DarkSky International's certified-places programme, or is matched against NPS night-sky material. The certification year is treated as verified only when we can identify it from those sources.
• Bortle darkness is established from the park's certification status, published night-sky descriptions, remoteness from major light domes, elevation, and known regional sky quality. When a park-specific measured value is not published, we mark the Bortle value as (est.).
• Clear nights are established from regional climate patterns and desert, mountain, coastal, or eastern-forest sky reliability. Where there is no published park-level clear-night percentage, we use a transparent regional estimate and mark it as (est.).
• The default table keeps the highest-confidence certified set first. The additional-parks view is useful for inspiration, but it mixes in units where one or more inputs still need stronger source confirmation.
• Download the CSV to see every value, including which ones are estimated.

Sources. DarkSky International certified-places registry, NPS Night Skies program, Open-Meteo for the forecast, sunrise-sunset.org for twilight times, and Sky & Telescope for the Bortle dark-sky scale.

A forecast of a chaotic sky is odds, not a promise. Always check a current local forecast before you drive out.

The town ranking is designed for planning a stargazing trip, not judging the sky from the middle of town. Each score combines measurable data with destination scoring, so the table reflects both the conditions around a town and how practical it is as a base for visitors.

• Sky Darkness Score is a composite score based on recognised dark-sky designations, nearby protected landscapes, observatory regions and local light-pollution context. Towns score better when they sit in or beside low-light areas.
• Average Cloud Cover uses location-based long-run cloud data rather than a single night's forecast. Cloudier places score lower because even very dark skies are less useful if clear nights are rare.
• Nearby dark-sky areas reward towns close to recognised viewing spots, so visitors can stay, eat or refuel in town, then drive a short distance to darker skies.
• Trip Ease Score is a destination score based on how realistic the town is as a visitor base, including places to stay, eat, refuel or start a night-sky drive from.
• Elevation uses location-based elevation data as a supporting factor because higher locations can have clearer, drier air, but it does not outweigh darkness or clouds.
• US and UK towns are ranked separately because climate, settlement patterns and access to dark-sky landscapes are very different in each country. The ranking should be read as a travel-planning comparison, not as a claim that every score comes from one single official dataset.

Sources. Dark-sky status and recognised viewing areas are checked against DarkSky International Places, CPRE dark skies resources and local park or observatory information. Cloud and elevation inputs use public climatology and mapping sources, including NASA POWER and national elevation data where available.